Action 1 - Calibration and Characteristics of Radiometers.- The implications for calibration and field use of non-ideal cosine behaviour in Kipp and Zonen CM-5 pyrananeters.- Action 2 - Reference Years.- Short reference years with adjusted measured data.- Establishment of short reference years for calculation of annual solar heat gain or energy consumption in residential and commercial buildings.- SRY production by means of stochastic models.- Short reference year, SRY.- Action 3. 1 - Global Irradiation on Horizontal Plane - Definition of Radiation Climate Zones.- Heliothermic indexes for the evaluation of the potential of solar energy.- Action 3. 2 - Global Irradiance on Tilted Planes - Direct Irradiation on Horizontal and Tilted Planes - Calculation of Turbidity Factor.- Classification of radiation sites in terms of different indices of atmospheric transparency.- Parameterization of radiation fluxes as function of solar elevation, cloudiness and turbidity.- Diffuse sky radiation on tilted surfaces.- Climatological values of solar irradiation on the horizontal and several inclined surfaces at De Bilt.- Development of methods - Analysis of solar radiation data of a high altitude station (1 580 m).- A statistical analysis of the components of solar radiation on a vertical south-facing surface.- Development of a systematic method for the prediction of solar radiation on inclined planes.- Calculation method for the radiation data on inclined surfaces and calculated atlas data.- Empirical study of the angular distribution of sky radiance and of ground reflected radiation fluxes.- Estimation of hourly solar irradiation over the UK.- Action 3. 3 - Statistical Analysis of Meteorological Data.- Analysis of short time data of irradiation on inclined planes.-Solar energy recovered by a flat plate collector.- Statistical distribution of solar radiation (hourly sums) : cumulative frequency curves.- Statistical analysis of solar radiation data of a high altitude station.- Studies of relationships between inclined surface irradiation, temperature and wind speed.- Action 3. 4 - Sensitivity Analysis of the Useful Energy Output from Solar Converters as a Function of the Type and Time-Step of Meteorological Data.- Report of action participant.- Action 4. 1 - Improvement of Measurements in National Networks of Global, Direct, Diffuse Irradiance and Irradiance on Inclined Surfaces.- Variability in space of solar radiation.- Improvement of measurement of diffuse solar radiation.- Progress toward establishing a comprehensive solar radiation data and calibration center in Greece.- Solar radiation in Italy.- Improvement of radiation network.- Investigation of the accuracy of shading ring corrections applied in the measurement of diffuse solar radiation.- The extension and improvement of the UK radiation network.- Actin 4. 2 - Special Measurements.- Study of I. R. radiation from the sky.- The flux density of radiation energy originating from the circumsolar sky measured at groundbased stations.- Special measurements of radiation in high altitude station.- Installation of equipment to measure the separate components of global solar radiation on a vertical surface.- Acticnv 4. 3 - Satellite Measurements.- Determination of the global radiation and of cloudiness from satellite data.- Satellite image analysis.- Heliosat project: estimation of global radiation from satellite using a statistical approach.- List of Participants.